1. Field of the Invention
The invention relates to a burner for a heat generator, in particular for a gas turbine.
2. Description of the Related Art
EP 797 051 A2 discloses a burner for a gas turbine. For better understanding, this burner is reproduced in FIG. 1. In this burner, which essentially comprises a swirl generator for a combustion-air flow and means for spraying a fuel into the combustion-air flow, a mixing section is arranged downstream of the swirl generator referred to. This mixing section, inside a first part of the section, has a number of transition passages which run in the direction of flow and ensure that the flow formed in the swirl generator is passed over smoothly into a downstream mixing tube. The outlet plane of this mixing tube relative to the combustion chamber is formed with a breakaway edge and a radius, the breakaway edge serving to stabilize and enlarge a backflow zone forming downstream. The breakaway edge and the radius are shown by FIG. 2, which is likewise taken from the publication EP 797 051 A2 and is reproduced here for clarification. Due to the configuration of this burner with the breakaway edge and the radius, a round flame is produced. A plurality of these burners are arranged in an annular manner around the axis of rotation of the gas turbine. However, a disadvantage of this prior art is that a relatively large number of burners are required due to the round flame shape, a factor which entails a cost disadvantage. The burners must be at a minimum distance from the combustion-chamber wall in order not to overheat the latter. On the other hand, the burners must be at a minimum distance from one another in order to permit a uniform temperature distribution and a good cross-ignition behavior.
The aim of the invention is to overcome the abovementioned disadvantages. The invention achieves the object of conceiving a burner with which the requisite number of burners of a combustion chamber is reduced, although the minimum distance of the burners from the combustion-chamber wall and the temperature distribution or the cross-ignition behavior are to remain the same.
According to the invention, this is achieved in a burner according to the preamble of the independent claim in that the radius is variable over the circumference of the mixing tube.
The radius is advantageously made in such a way that an ellipsoidal transition from the mixing tube to the combustion chamber and consequently an ellipsoidal flame are obtained. The flame shape may thus be varied from a round shape to an ellipse, the ratio of flame width to flame height being 3 at most. Due to a substantially larger width of the flame, the number of burners is markedly reduced while the design criteria remain the same. With this invention, it is also possible to convert existing gas turbines in a simple manner. Owing to the fact that the flame can be configured so as to be variable from a round shape to an ellipsoidal shape, the flame shape may also be individually adapted to a geometrical form of an existing gas turbine.